1. Field of the Invention
The present invention relates to a method of preparing a composition to be sprayed on plant leaves or fruits for the purpose of preventing biological lesions caused by deficiency of calcium component, and specifically relates to a method capable of preparing a composition having an enhanced content of water-soluble calcium component.
2. Description of the Prior Art
Calcium component is quite important for plant growth causing translocation of nutrients and improvement in cell assimilation. Further, calcium component is effective in neutralizing organic acids formed in plant bodies, and deficiency thereof brings about acidification of the humor to result in a hindered synthesis or translocation of hydrocarbons. Calcium component is generally recognized as difficultly movable in plant bodies, being contained more in old leaves than in young leaves, and movable scarcely into fruiting bodies.
Biological lesions caused by the deficiency in calcium component include Bitter Pit of apple and Blossom-end rot incidence of tomato and Core rot incidence of celery or Chinese cabbage, for example. Calcium component existing in soil are not necessarily absorbed and utilized fully by plants, as will be apparent from the fact that biological lesion is caused by deficiency in calcium despite the soil was supplied beforehand with calcareous fertilizers.
In order to supplement the deficiency in calcium and to cope directly and aggressively with the biological lesion caused by deficiency in calcium, there is a method of rendering the calcium to be absorbed by spraying a water-soluble calcium component directly on plant leaves or fruits. The water-soluble calcium component employed generally is calcium chloride or calcium primary phosphate, however, these compounds are not satisfactory to plants for supplying them with calcium component, as the former sometimes causes phytotoxicity and the latter has problems of the inferior solubility and a lowered pH.
For solving the problem of inferior solubility, various calcium compounds of highly soluble in water have been proposed for compositions to be sprayed on plant leaves or fruits. There are proposed methods using, for example, calcium formate in JP-A-59-137384, calcium acetate in JP-A-60-260487 and calcium propionate in JP-A-4-202080. However, as these calcium compounds are rather expensive, it is desirous of having a method of preparing an inexpensive composition for spraying on plants, in which the composition has a calcium solubility equivalent to or larger than that of these calcium compounds and causes no phytotoxicity.
JP-A-4-8231 discloses a composition containing a water-soluble calcium component, a saccharide and an organic acid for spraying on plant leaves or fruits. The reference teaches that the organic acid is absorbed to lower the pH and acidifies the plant, the calcium component is absorbed and adjusts or neutralizes the lowered pH of the plant and the saccharide stimulates absorption of the calcium component by its effect on the osmotic pressure. As to preparation methods of the composition, mention is made in the Example as for adding an aqueous solution of an organic acid (propionic acid, citric acid) to an aqueous solution of monocalcium saccharose or adding a saccharide (glucose) to an aqueous solution of an organic acid (propionic acid, citric acid) calcium salt. However, the disclosed concentration of calcium component is 4.0% as CaO, and no mention is made on the intention or the method for enhancing the concentration of calcium component.
The present inventors gave attention to an increased solubility of calcium component in an aqueous solution of glucose, due to formation of a water soluble calcium complex when Ca(OH).sub.2 was added to the glucose solution. A further study on the increased solubility made them find out that it was possible to increase the solubility of calcium component and stability of the solution by means of preparing firstly an aqueous solution containing glucose and an organic acid, and then adding to the solution calcium hydroxide or a substance capable of forming calcium hydroxide upon hydration.